The present invention relates generally to the field of mass storage devices. More particularly, this invention relates to a combined linear bearing and vacuum stiffener for use with a high density disc drive servo track writing apparatus.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc drive housing, a disc that is rotated, an actuator assembly that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
To read and write data to the disc drive, the actuator assembly includes one or more arms that support the transducer over the disc surface. The actuator assembly is selectively positioned by a voice coil motor which pivots the actuator assembly about a pivot shaft secured to the drive housing. The disc is coupled to a motorized spindle which is also secured to the housing. During operation, the spindle provides rotational power to the disc. By controlling the voice coil motor, the actuator arms (and thus the transducers) can be positioned over any radial location along the rotating disc surface.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equalize so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on portions of the storage disc referred to as tracks. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto the track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write to or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is often divided between several different tracks. While most storage discs utilize a multiplicity of concentric circular tracks, other discs have a continuous spiral forming a single track on one or both sides of the disc.
During manufacture, servo feedback information is encoded on the disk and subsequently used to accurately locate the transducer. The servo information is used to locate the actuator assembly/transducer head at the required position on the disc surface and hold it very accurately in position during a read or write operation. The servo information is written or encoded onto the disc with a machine commonly referred to as a servo track writer (hereinafter STW). At the time the servo information is written, the disc drive is typically at the xe2x80x9chead disk assemblyxe2x80x9d (hereinafter HDA) stage. The HDA includes most of the mechanical drive components but does not typically include all the drive electronics. During the track writing process, the STW precisely locates the transducer heads relative to the disc surface and writes the servo information thereon. Accurate location of the transducer heads is necessary to ensure that the track definition remains concentric. If the servo track information is written eccentrically, the position of the transducer head during subsequent operation will require relatively large, constant radial adjustments in order to maintain placement over the track center. When the tracks are sufficiently eccentric, a significant portion of the disk surface must be allotted for track misregistration. Accordingly, overall track density is degraded and disc drive capacity is reduced.
In order to ensure proper writing of servo information, STWs utilize an external, closed loop positioning system that precisely positions the transducer head during servo track writing. The positioning system comprises a contact member that engages the actuator assembly, a position indicator which indicates the position of the contact member, and a displacing mechanism which repositions the contact member based on feedback from the position indicator. To ensure accurate positioning, various position indicators are used (e.g., mechanical, capacitive, and optical transducers to name a few). The STW further includes the required circuitry for writing the servo information to the disc surface via the transducer heads.
As demand for higher capacity drives grows, manufacturers are constantly seeking to increase drive capacity by increasing track density. That is, by increasing the density or xe2x80x9ctracks per inchxe2x80x9d (TPI), a greater number of discreet tracks can be encoded on a given disc surface. However, higher track density requires more efficient use of the disc surface. Accordingly, track misregistration due to eccentricities in track formation must be minimized in order to maximize TPI (and thus disc capacity).
While it is advantageous to maintain substantial concentricity during the servo track writing process, many factors adversely impact the STW""s ability to write servo information concentrically. For instance, induced resonance in the STW itself can adversely affect the track writing operation. Further, vibrations in the spindle or actuator components (e.g., imperfect bearings) may also produce nonrepeatable track writing errors. Still yet another problem with current STWs is oscillations in the HDA itself (i.e., independent deflection of the actuator and spindle relative to the STW). The present invention is directed to reducing these problems, especially the effects of component deflection, and the remainder of this discussion will focus on the same.
Most current STWs support the HDA by engaging a plurality of points on the external drive housing. When the HDA is so engaged, the spindle and actuator are restrained only by the internal structure of the HDA (i.e., the drive housing). Still other HDAs fasten the drive cover to the pivot shaft and a spindle shaft to provide additional support thereto. However, these STW/HDA configurations still produce drives with limited track densities not because of the STW""s positioning accuracy but rather because of the non-repeatable deflection and vibration of the HDA components.
Another problem encountered in designing the STW of the present invention was how to ensure that the HDA could be repeatably and correctly loaded therein. If improperly loaded, errors in the servo track writing process may occur. While utilizing a technician to monitor and manually guide the HDA during the loading process is possible, it is also time consuming and prone to operator error. Accordingly, an apparatus that can precisely and repeatably place the HDA within the STW without operator input is desirable.
Yet another problem is how to immobilize the HDA once it is properly loaded within the STW. While various mechanical clamping systems are known, some may adversely affect the precise position of the HDA. Others may apply an uneven clamp load which can adversely affect the servo track writing process. A clamping system that may evenly and adequately secure the HDA without adversely affecting its location is therefore desirable.
Accordingly, what is needed is an apparatus and method for use with an STW that minimizes relative deflection between the components of the HDA during the track writing process. In particular, what is needed is a way to reduce HDA component deflection sufficiently to allow greater track densities to be formed on a given disk surface. What is further needed is an improved apparatus for loading and securing the HDA in place within the STW. The present invention addresses these needs.
In one embodiment, a vacuum block for use with a guide surface is provided wherein the vacuum block includes a vacuum stiffener having a recessed portion adapted to fluidly coupled to a vacuum source. The vacuum block further includes an air bearing extending around a periphery of the recessed portion wherein the air bearing is adapted to fluidly couple to a pressurized air source. In a first configuration, the vacuum source and the pressurized air source are activated simultaneously to elevate the vacuum block from the guide surface on an air film. In this configuration, the air bearing is preloaded by the vacuum stiffener. In a second configuration, the pressurized air source is deactivated to permit the vacuum stiffener to vacuum couple the vacuum block to the guide surface.
In another embodiment, a method for displacing and securing a vacuum block relative to a guide surface is disclosed. The method includes providing a vacuum block wherein the vacuum block includes a vacuum stiffener. The vacuum stiffener has a recessed portion adapted to fluidly coupled to a vacuum source. Also provided is an air bearing surface extending around a periphery of the recessed portion, wherein the air bearing surface is adapted to fluidly couple to a pressurized air source. The method further includes the step of activating the pressurized air source wherein a bearing force is produced between the guide surface and the air bearing surface such that an air film develops therebetween. The vacuum source is activated to a first vacuum pressure wherein the vacuum source provides a preload force opposite the bearing force. Thereafter, the pressurized air source is deactivated and the vacuum source is maintained to vacuum-couple the vacuum block to the guide surface in a predetermined location.
In yet another embodiment, a servo track writing apparatus for securing a head disc assembly (HDA) during a servo track writing process is provided. The apparatus includes a base, a fixed block assembly attached to the base and a basket assembly opposing the fixed block assembly. The basket assembly further includes a movable carriage having a basket adapted to receive the HDA, and a vacuum block adapted to selectively permit both precise movement of the movable carriage relative to the base and to permit vacuum coupling of the movable carriage thereto. The apparatus also includes a displacing device adapted for moving the carriage toward the fixed block assembly and a loading device adapted for loading the carriage against the fixed block assembly.
In still yet another embodiment, an apparatus for precisely locating a moving member relative to a guide surface in a servo track writer (STW) is provided. The apparatus includes an air bearing adapted to generate an air film between the moving member and the guide surface, and a device for stiffening the air bearing.
Advantageously, the present invention provides an STW having an air bearing and vacuum stiffener that permits precise movement of the vacuum block relative to a guide surface without the need for a second, opposing air bearing or similar preloading device. In addition, by operating the vacuum stiffener independently from the air bearing, the vacuum stiffener may also be used to vacuum couple the vacuum block to the guide surface, eliminating the need for a separate clamping device. Accordingly, the HDA may be loaded into and secured within the STW without manual operator intervention. The result is more accurate HDA placement and, ultimately, more efficient servo track writing.